The invention relates to conveyor lubricants and lubricant compositions, to methods of use, for example, to treat or lubricate a container(s) and conveyor surfaces or system for containers. The invention also relates to containers and conveyor surface or system treated with a lubricant or lubricant composition. The container is, for example, a food or beverage container.
The invention relates to maintaining the physical and structural integrity of shaped thermoplastic articles by inhibiting stress cracking. Many thermoplastic articles are formed using thermal methods at elevated temperatures. When formed into simple, regular or complex shapes and cooled, significant stress can remain in the thermoplastic material. The stress is undesirably relieved in the form of cracking. Such stress cracking can be substantially promoted if the stressed thermoplastic is contacted with a material that tends to promote stress cracking. The lubricating methods and compositions of the invention are intended to passivate, inhibit or prevent the undesirable interaction between the stressed thermoplastic and stress cracking promoters.
In commercial container filling or packaging operations, the containers typically are moved by a conveying system at very high rates of speed. In current bottling operations, copious amounts of aqueous dilute lubricant solutions (usually based on ethoxylated amines or fatty acid amines) are typically applied to the conveyor or containers using spray or pumping equipment. These lubricant solutions permit high-speed operation (up to 1000 containers per minute or more) of the conveyor and limit marring of the containers or labels, but also have some disadvantages. For example, aqueous conveyor lubricants based on fatty amines typically contain ingredients that can react with spilled carbonated beverages or other food or liquid components to form solid deposits. Formation of such deposits on a conveyor can change the lubricity of the conveyor and require shutdown to permit cleanup. Some aqueous conveyor lubricants are incompatible with thermoplastic beverage containers made of polyethylene terephthalate (PET) and other plastics, and can cause stress cracking (crazing and cracking that occurs when the plastic polymer is under tension) in carbonated beverage filled plastic containers. Dilute aqueous lubricants typically require use of large amounts of water on the conveying line, which must then be disposed of or recycled, and which causes an unduly wet environment near the conveyor line. Moreover, some aqueous lubricants can promote the growth of microbes.
Thermoplastic materials have been used for many years for the formation of thermoplastic materials in the form of film, sheet, thermoformed and blow molded container materials. Such materials include polyethylene, polypropylene, polyvinylchloride, polycarbonate, polystyrene, nylon, acrylic, polyester polyethylene terephthalate, polyethylene naphthalate or co-polymers of these materials or alloys or blends thereof and other thermoplastic materials. Such materials have been developed for inexpensive packaging purposes. Thermoplastic materials are manufactured and formulated such that they can be used in thermoforming processes. Such thermal processing is used to form film, sheet, shapes or decorative or mechanical structures comprising the thermoplastic material. In such processes, the thermoplastic is heated to above the glass transition temperature (Tg) or above the melting point (Tm) and shaped into a desirable profile by a shaping die. After the shape is achieved, the material is cooled to retain the shape. The cooling of such materials after shaping can often lock-in stresses from the thermal processing. Filling such a container with carbonated beverage can place large amounts of stress in the bottle structure. Most thermoplastic materials when stressed react undesirably to the stress and often relieve the stress through cracking. Such cracking often starts at a flaw in the thermoplastic and creeps through the thermoplastic until the stress is relieved to some degree.
Such stress cracking can be promoted by stress cracking promoter materials. Thermoplastics that are highly susceptible to stress cracking include polyethylene terephthalate, polystyrene, polycarbonate and other thermoplastics well known to the skilled materials scientist. The mechanism of stress crack promotion, initiation and propagation has been discussed and investigated but not clearly delineated. Stress cracking can be explained by discussing interactions between stress cracking promoters and the polymeric chains that make up the thermoplastic material. The stress cracking promoters are believed to cause one or more chain to move relative to another chain, often initiated at a flaw in the plastic, resulting in cracking. Other theories include a consideration of the chemical decomposition of the thermoplastic material or (e.g.) a base catalyzed hydrolysis of the polyester bond resulting in weakened areas in the thermoplastic resulting in associated cracking. Lastly, the thermoplastic materials are believed to absorb more hydrophobic materials that soften the thermoplastic and, by reducing the strength of the thermoplastic, can promote the growth and propagation of stress cracking.
Regardless of the theory of the creation and propagation of stress cracks, thermoplastics manufacturers are well aware of stress cracking and have sought to develop thermoplastic materials that are more resistant to stress cracking. Stress cracking can be reduced by sulfonating the bulk thermoplastic after formation into a final article. Further, the manufacture of containers in two, three, four or other multilayer laminate structures is also believed to be helpful in reducing stress cracking. However, we have found that even the improved polymer materials can be susceptible to stress cracking. Further, certain commonly used container structures including polystyrene materials, polycarbonate materials, polyethylene terephthalate materials tend to be extremely sensitive to stress cracking promoters particularly when pressurized or used at high altitudes and can during manufacture, use or storage quickly acquire a degree of stress cracking that is highly undesirable.
One technology involving significant and expensive stress cracking involves the manufacture of polyethylene terephthalate (PET) beverage containers. Such beverage containers are commonly made in the form of a 20 oz, one, two or three liter container for carbonated beverages. Alternatively, a petaloid design can be formed into the polyester to establish a stable base portion for the bottle. In both formats, the polyester beverage container can have significant stress formed in the shaped bottom portion of the bottle. The stresses in the pentaloid structure tend to be greater because of the larger amorphous region and more complex profile of the container base.
Polyester beverage containers are made in a two step process. Melt thermoplastic is formed into a preform. Such preforms are relatively small (compared to the finished bottle) comprising the threaded closure portion and a xe2x80x9ctest tubexe2x80x9d like shape that is blow molded into a final bottle conformation. In manufacturing the beverage containers, the preform is inserted into a blow molding apparatus that heats the preform and, under pressure, inflates the softened preform forcing the preform into a mold resulting in the final shape. The finished beverage containers are shipped to a filling location. The containers are filled with carbonated beverage in a filling apparatus that involves a moving conveyor surface that transports the container during filling. The conveyor structure comprises a filling station, a capping station and ends at a packing station. While on the conveyor, the containers are exposed to an environment that contains residual cleaners and conveyor lubricants containing organic and inorganic stress cracking components that can interact with the polyester thermoplastic of the container. Stress cracking can appear as fine cracking that typically forms axially around the center of the bottle. The appearance of any stress cracking is undesirable. Should beverage containers stress crack, the pressure of the carbonated beverage can often cause the beverage container to explode and spill the beverage contents in the processing plant, transportation unit, warehouse or retail outlet. Such spillage poses health problems, sanitation problems, maintenance problems and is highly undesirable to manufacturers and retail merchants.
Initially such conveyor systems were lubricated using dilute aqueous lubricant materials. Typical early conveyor lubricants comprise substantially soluble sodium salt of the fatty acid or sodium salt of linear alkane sulfonate which acted to both lubricate and at least to some degree, clean the conveyor surfaces. Representative examples of such lubricants are found in Stanton et al., U.S. Pat. No. 4,274,973 and Stanton, U.S. Pat. No. 4,604,220. When conventional aqueous conveyor lubricant compositions were applied to conveyors for polyester beverage containers, the lubricants were found to be significant stress crack promoting materials. No clear understanding of the nature of stress crack promotion is known, however, the lubricant compositions containing basic materials (caustic and amine compounds) appear to be stress crack promoters. Such materials include aqueous soluble sodium salts, aqueous soluble amine compounds, and other weak to strong aqueous soluble bases have been identified as stress crack promoters. Other stress cracking promoters include solvents, phenols, strong acids, alcohols, low molecular weight alcohol ethoxylates, glycols and other similar materials.
A series of allegedly stress crack inhibiting substantially soluble aqueous lubricants were introduced including Rossio et al., U.S. Pat. Nos. 4,929,375 and 5,073,280; and Wieder et al., U.S. Pat. No. 5,009,801. These patents assert that certain substituted aromatic compounds, certain couplers and saponifying agents and certain amine compounds can inhibit stress cracking in appropriately formulated materials. Other patents, including Person Hei et al., U.S. Pat. Nos. 5,863,874 and 5,723,418; Besse et al., U.S. Pat. No. 5,863,871; Gutzmann et al., U.S. Pat. Nos. 5,559,087 and 5,352,376; Liu et al., U.S. Pat. No. 5,244,589; Schmitt et al., U.S. Pat. No. 5,182,035; Gutzmann et al., U.S. Pat. No. 5,174,914; teach conveyor lubricants that provide adequate lubrication, cleaning and inhibit stress cracking.
In many applications, known improved stress cracking resistant thermoplastic materials cannot be used for reasons of cost or poor processability properties. A substantial need exists for improved methods of preventing stress cracking in shaped thermoplastic materials in any environment. Important harsh environments include a stress crack promoter.
Containers are receptacles in which materials are or will be held or carried. Containers are commonly used in the food or beverage industry to hold food or beverages. Often lubricants are used in conveying systems for containers, to ensure the appropriate movement of containers on the conveyor.
In the commercial distribution of many products, including most beverages, the products are packaged in containers of varying sizes. The containers can be made of paper, metal or plastic, in the form of cartons, cans, bottles, Tetra Pak(trademark) packages, waxed carton packs, and other forms of containers. In most packaging operations, the containers are moved along conveying systems, usually in an upright position, with the opening of the container facing vertically up or down. The containers are moved from station to station, where various operations, such as filling, capping, labeling, sealing, and the like, are performed. Containers, in addition to their many possible formats and constructions, may comprise many different types of materials, such as metals, glasses, ceramics, papers, treated papers, waxed papers, composites, layered structures, and polymeric materials.
Lubricating solutions are often used on conveying systems during the filling of containers with, for example, beverages. There are a number of different requirements that are desirable for such lubricants. For example, the lubricant should provide an acceptable level of lubricity for the system. It is also desirable that the lubricant have a viscosity which allows it to be applied by conventional pumping and/or application apparatus, such as by spraying, roll coating, wet bed coating, and the like, commonly used in the industry.
In the beverage industry, the lubricant must be compatible with the beverage so that it does not form solid deposits when it accidentally contacts spilled beverages on the conveyor system. This is important since the formation of deposits on the conveyor system may change the lubricity of the system and could require shutdown of the equipment to facilitate cleaning.
The lubricant must be such that it can be cleaned easily. The container and/or the conveyor system may need to be cleaned. Since water is often in the cleaning solution, ideally the lubricant has some water-soluble properties.
Currently, containers, including polyethylene terephthalate (PET) bottles, and conveying systems for containers are often contacted with a volume of a dilute aqueous lubricant to provide lubricity to the container so that it can more easily travel down the conveyor system. Many currently used aqueous-based lubricants are disadvantageous because they are incompatible with many beverage containers, such as PET and other polyalkylene terephthalate containers, and may promote stress cracking of the PET bottles.
Furthermore, aqueous based lubricants are in general often disadvantageous because of the large amounts of water used, the need to use a wet work environment, the increased microbial growth associated with such water-based systems, and their high coefficient of friction. Moreover, most aqueous-based lubricants are incompatible with beverages.
Flooding a conveyor surface with a substantial proportion of aqueous lubricant typically occurs on food container filling or beverage bottling lines. Sufficient lubricant is used such that the lubricant is not retained entirely by the surface of the conveyor but tends to flow from the surface of the container, drip onto a conveyor support members and the surrounding environmental area around the conveyors. Further, sufficient amounts of lubricant are applied to the conveyor and other mechanisms of the plant under such conditions that a substantial foam layer of lubricant can form on the surface of the conveyor. As much as one inch (about 2.5 cm or more) thick of lubricant foam can contact a substantial portion of the base of a food container such as polyethylene terephthalate beverage bottle. We have found that current methods of lubricating such containers are wasteful of the lubricant material since a substantial proportion of the materials is lost as it leaves the container surface. Further, substantial proportions of the lubricant remain on the container and are carried from the conveyor as the food packaging or beverage-bottling operations are continued. A substantial need exists for approved methods that waste little or no lubricant during packaging or bottling operations.
The tendency of polyester (PET) beverage containers to crack or craze is promoted by the presence of a number of common lubricating materials in contact with a substantial proportion of the surface of a polyester beverage container under pressure. The stress arises during manufacture of the polyester bottle from a preform. The stress is locked into the beverage container during manufacture and is often relieved as the lubricant materials contact the bottle. Lubricant materials appear to promote movement of the polyester molecules with respect to each other, relieving stress and leading to the creation of stress cracking. We have found that the degree of stress cracking is attributable, at least in part, to the amount of surface area of the bottle contacted by the lubricant. We have found in our experimentation that limiting the amount of surface area of the bottle that comes in contact with the lubricant can substantially improve the degree of stress cracking that occurs in the bottle material. Clearly, a substantial need exists to develop lubricating methods that result in the minimum amount of lubricant contact with the surface of the food container.
We have surprisingly found a number of techniques that can passivate containers to stress cracking and we have found unique formulations of lubricant materials that can be used on conveyor lines to lubricate the high speed filling of such bottles without substantial stress cracking.
One aspect of the invention involves a method of use of a liquid hydrocarbon lubricant. A next aspect includes forming a liquid lubricant for a polyethylene terephthalate beverage container. The lubricant comprises, in a liquid medium, a liquid hydrocarbon oil composition and optionally a lubricant additive composition. A further aspect of the invention involves contacting a conveyor with a liquid dispersion of a liquid hydrocarbon oil while simultaneously contacting the conveyor with a second lubricant composition. Lastly, an aspect of the invention comprises a method of operation a conveyor by forming a lubricant film on the conveyor, the film comprising a liquid medium and a liquid hydrocarbon oil composition. The lubricant film can be made from a single composition comprising all needed components or from a two (or more) package lubricant in which the liquid hydrocarbon oil material is separately packaged as a stress cracking inhibitor. In such a system the lubricant components can be packaged separately form the liquid hydrocarbon oil package.
We have surprisingly found that a liquid hydrocarbon oil composition can also passivate a shaped thermoplastic to stress cracking. We found a number of substantially hydrophobic materials such as oils, solid lubricant materials, silicone materials, and other materials that are not typically dispersed or suspended in aqueous solutions that can adequately passivate beverage containers, lubricate conveyor lines operating at high speeds and can operate successfully without promoting significant stress cracking in the container. Preferred materials that can be used in such an environment include oils including hydrocarbon oils, fatty oils, silicone oils, and other oily or hydrocarbon lubricants from a variety of sources. One particularly useful form of the lubricant is the form of a silicone material that can be used in common lubricant compositions. Further, one particularly advantageous form of such lubricants is in the form of an aqueous suspension of the lubricant that is in a formulation that can readily change phase from a suspended or dispersed lubricant material in the aqueous phase to a separate lubricating phase of the lubricant material not dispersed or suspended in the aqueous medium. The liquid hydrocarbon oil can be used in a thermoplastic shaped articles for the purpose of preventing stress cracking even when exposed to stress cracking promoting materials. For the purpose of the application, liquid hydrocarbon oil means a solvent-free hydrocarbon oil. Such solvents include aqueous materials and light, relatively volatile (compared to the oil) organic liquids. We believe that the oil can protect the bottles from chemical attack by a stress crack promoter at any time during and after manufacture. The oil can protect the bottles inside and out. Carbonated beverages, and particularly club soda, are known stress crack promoters that at virtually any time after manufacture can cause stress cracking when in contact with the outside of a beverage bottle due to high alkalinity and high stress. Other materials can stress crack such as manufacturing and packaging materials, materials used in filling operations, materials contained in the thermoplastic and materials contacting the thermoplastic after filling during storage and use. Contaminants found in the container coolers and warmers (biocides, alcoholic fermentation by-products, and build-up of alkalinity due to evaporation) can be significant stress crackers. Preferably such an oil is also substantially free of particulate lubricant materials such as MoS2, alkali metal and alkaline earth metal salts, etc.
The thermoplastic material can be combined with liquid hydrocarbon oil in a variety of processes and structures. The thermoplastic material can be shaped with liquid hydrocarbon oil in the shaping die as a release agent. When formed into a shaped article, the liquid hydrocarbon oil, present on the surface of the thermoplastic can inhibit stress cracking. A second aspect in the invention includes contacting the shaped article with a liquid hydrocarbon oil material to form a thin coating of the liquid hydrocarbon oil on the surface of the container. A variety of techniques can be used including spraying, wiping, dipping, fogging, etc. with a liquid hydrocarbon oil containing composition to result in a thin coating on the surface of the container. The thin coating can act as a barrier to crack promoters preventing stress crack formation. Another aspect of the invention involves forming a coating on the shaped article with liquid hydrocarbon oil just before or just after the time of use. The typical use involves charging the container with typically liquid contents. Such contents can be liquid, gaseous or solid. A further aspect of the invention involves forming a coating of the liquid hydrocarbon oil on the thermoplastic article just prior to contact with a stress crack promoter.
One preferred mode of action involves methods of forming such a coating on a polyethylene terephthalate beverage container just prior to beverage filling operations. Lastly, an aspect of the invention involves forming a coating on the shaped thermoplastic article just after contact with a stress cracking promoter to reduce the undesirable impact of the promoter on the thermoplastic material.
We have found that the problems inherent in conventional aqueous lubrication of conveyor systems used in food packaging and beverage bottling can be substantially improved using a continuous thin film lubricant layer formed on a conveyor surface. The lubricant layer is maintained at a thickness of less than about 3 millimeters, preferably about 0.0001 to 2 mm, with an add on of lubricant on the surface of less than about 0.05 gms-inxe2x88x922, preferably about 5xc3x97104 to 0.02 gms-inxe2x88x922, most preferably about 2xc3x9710xe2x88x924 to 0.01 gms-inxe2x88x922. Such a thin lubricating film of the lubricant on the conveyor provides adequate lubrication to the conveyor system but ensures that the lubricant cannot foam, does not flow from the conveyor surface and contacts the absolute minimum surface area of the food container such as the beverage bottle as possible. Such a thin film lubricant maintains significant lubrication while avoiding waste of the lubricant composition and avoiding stress cracking promotion. We have found that one mode of formation of the liquid lubricant compositions of the invention are in the form of an aqueous oil emulsion wherein the aqueous phase comprises about 10 to 50 wt % of the lubricant. The form of the emulsion can be either water in oil or oil in water emulsion. One preferred format of the emulsion is a phase unstable emulsion such that the emulsion separates forming an oil layer on top of a water layer which is then, in turn, contact with the conveyor surface. The methods of the invention can be used to convey virtually any food container on a conveyor line, but is particularly adapted to transporting both steel and aluminum cans and thermoplastic beverage containers such as polyethylene terephthalate beverage containers. Common PET beverage containers are formed with a pentaloid base having a five lobed structure in the base to provide stability to the bottle when it is placed on a surface. The contact with the lubricant on the pentaloid base must be minimized. We have found that using a thin film of emulsion lubricant, that less than about 10 to 300 mm2, preferably 20 to 200 mm2 of the surface of the bottle is contacted with lubricant. Certainly, the height of the lubricant in contact with the bottle is less than 3 millimeters. The motion of the conveyor, the tendency of the bottles to rock or move while being conveyed and the other aspects of relative movement at the bottle conveyor interface affect the height of the lubricant on the bottle. The methods of this invention are primarily directed to conveyor operations and do not involve any change in shape of the container arising from forming operations. The desirable coefficient of friction of the conveyor lubricant is about 0.1 to about 0.14.
Another aspect of the invention provides a method for lubricating the passage of a container along a conveyor comprising applying a mixture of a water-miscible silicone material and a water-miscible lubricant to at least a portion of the container-contacting surface of the conveyor or to at least a portion of the conveyor-contacting surface of the container. The present invention provides, in another aspect, a lubricated conveyor or container, having a lubricant coating on a container-contacting surface of the conveyor or on a conveyor-contacting surface of the container, wherein the coating comprises a mixture of a water-miscible silicone material and a water-miscible lubricant. The invention also provides conveyor lubricant compositions comprising a mixture of a water-miscible silicone material and a water-miscible lubricant. During some packaging operations such as beverage container filling, the containers are sprayed with warm water in order to warm the filled containers and discourage condensation on the containers downstream from the filling station. This warm water spray can dilute the conveyor lubricant and reduce its lubricity.
Still another aspect of the invention provides a method for lubricating the passage of a container along a conveyor comprising applying a phase-separating mixture of a hydrophilic lubricating material and an oleophilic lubricating material whose specific gravity is less than or equal to the specific gravity of the hydrophilic lubricating material, to at least a portion of the container-contacting surface of the conveyor or to at least a portion of the conveyor-contacting surface of the container. Prior to application to a conveyor or container, the mixture is agitated or otherwise maintained in a mixed but unstable state. Following application, the hydrophilic lubricating material and oleophilic lubricating material tend to undergo phase-separation, and we believe that the oleophilic lubricating material may tend to form a continuous or discontinuous film atop the hydrophilic lubricating material thereby providing a water-repelling lubricating layer having reduced water sensitivity.
The invention provides, in another aspect, a lubricated conveyor or container, having a lubricant coating on a container-contacting surface of the conveyor or on a conveyor-contacting surface of the container, wherein the coating comprises phase-separated layers of oleophilic lubricating material and a hydrophilic lubricating material. The invention also provides lubricating compositions for use on containers and conveyors, comprising an unstable mixture of an oleophilic lubricating material and a hydrophilic lubricating material. Therefore, it was an object of the present invention to provide an alternative to aqueous-based lubricants currently used in the container industry, which overcomes one or more of the disadvantages of currently used aqueous-based lubricants.
It was also an object of the invention to provide methods of lubricating containers, such as beverage containers, that overcome one or more of the disadvantages of current methods.
There is also provided a process comprising moving beverage containers on a conveyor that has been lubricated with a substantially non-aqueous lubricant or lubricant composition.
There is also provided in accordance with the invention, a conveyor used to transport containers, which is coated on the portions that contact the container with a substantially non-aqueous lubricant or lubricant composition.
There is also provided a composition for preventing or inhibiting the growth of microorganisms on a container or a conveyor surface for a container, comprising a substantially non-aqueous lubricant and an antimicrobial agent.
There is also provided a substantially non-aqueous lubricant and a substantially non-aqueous lubricant composition, and process for cleaning the lubricant or lubricant composition from the container and conveyor system.
Further objects, features, and advantages of the invention will become apparent from the detailed description that follows.
The compositions used in the invention can be applied in relatively low amounts and do not require in-line dilution with significant amounts of water. The compositions of the invention provide thin, substantially non-dripping lubricating films. In contrast to dilute aqueous lubricants, the lubricants of the invention provide drier lubrication of the conveyors and containers, a cleaner and drier conveyor line and working area, and reduced lubricant usage, thereby reducing waste, cleanup and disposal problems.
The present invention provides in one aspect a container or conveyor for containers whose surface is coated at least in part with a thin, substantially non-dripping layer of a water-based cleaning agent-removable lubricant.
The invention also provides a process for lubricating a container, comprising applying to at least a part of the surface of the container a thin, substantially non-dripping layer of a water-based cleaning agent-removable lubricant.
The invention also provides a process for lubricating a conveyor system used to transport containers, comprising applying a thin, substantially non-dripping layer of a water-based cleaning agent-removable, substantially non-aqueous lubricant to a conveying surface of a conveyor, and then moving containers, such as beverage containers, on the conveyor.
The compositions and methods used in the invention can be applied in relatively low amounts and with relatively low or no water content, to provide thin, substantially non-dripping lubricating films. In contrast to dilute aqueous lubricants, the lubricants of the invention provide drier lubrication of the conveyors and containers, a cleaner conveyor line and reduced lubricant usage, thereby reducing waste, cleanup and disposal problems.
Further features and advantages of the invention will become apparent from the detailed description that follows.